The objectives of this research are the quantitative determination of the coordination and complexing properties of the trivalent lanthanide cations, and the subsequent application of this information to the study of these ions with ligands of physiological importance. the lanthanides are used extensively as nuclear magnetic resonance (NMR) chemical shift reagents, as probes of biological systems requiring a metal-ion for activity, as binding agents with ionophores and biological ligands, and in numerous industrial processes. The information sought includes the maximum coordination number at our conditions of measurement; the determination of variations, if any, of this value through the lanthanide series; the extent of competitive solvation and its correlation with ligand properties; the presence of inner-shell complexing and its dependence on anion and solvent properties; and in all cases, the quantitative determination of the structures of the species in solution. The experimental techniques to be used permit the direct observation of NMR signals for the components in the primary cation solvation shell, specifically, solvent ligands, anions, and in some systems, the metal ion itself, for example, lanthanum. In turn, these observations lead to the quantitative evaluation of the lanthanide coordination properties mentioned above. The measurements will be made using a Bruker AM-400 multinuclear, superconducting, Fourier transform NMR spectrometer. Depending on the salt and solvent system, the chemical shift, area, and linewidth techniques to be applied will involve the 1H, 13C, 15N, 31P, 35Cl, 81Br, 127I, and metal- ion nuclei where possible. Feasibility measurements with most of these nuclei have already been made.